Creatinine Clearance Calculator
The Formula That Refuses to Retire
Cockcroft-Gault was published in 1976, predates the equations that were meant to supersede it, and is still specified by name in the prescribing information of a long list of drugs. The reason is pragmatic rather than sentimental: many pharmacokinetic dosing studies were conducted using Cockcroft-Gault clearance as the reference, so the thresholds printed on those labels only mean what they say if you compute clearance the same way. Newer is not automatically compatible.
The Formula
The Cockcroft-Gault equation, exactly as implemented here:
Sex Factor = 0.85 for female, 1.0 for male
Three things are worth noticing. Clearance falls linearly with age, so every decade costs a fixed slice. It rises linearly with weight, which is why the choice of body weight to enter matters enormously. And it falls with the reciprocal of creatinine — doubling creatinine halves the estimate, no matter where you start.
Computed Clearance Reference
All values below were calculated with the formula above at a fixed 70 kg body weight:
| Age | Scr 0.8 (M / F) | Scr 1.0 (M / F) | Scr 1.5 (M / F) | Scr 2.0 (M / F) |
|---|---|---|---|---|
| 30 | 133.7 / 113.6 | 106.9 / 90.9 | 71.3 / 60.6 | 53.5 / 45.5 |
| 50 | 109.4 / 93.0 | 87.5 / 74.4 | 58.3 / 49.6 | 43.8 / 37.2 |
| 70 | 85.1 / 72.3 | 68.1 / 57.8 | 45.4 / 38.6 | 34.0 / 28.9 |
| 80 | 72.9 / 62.0 | 58.3 / 49.6 | 38.9 / 33.1 | 29.2 / 24.8 |
Creatinine (Scr) in mg/dL. Because clearance scales linearly with weight, a 50 kg patient's figure is these values × 50/70; a 90 kg patient's is these values × 90/70.
The Weight Question
The single largest source of disagreement between two people computing Cockcroft-Gault on the same patient is not the formula — it is which weight went into it. The 1976 paper used actual body weight, but applying actual weight in obesity inflates the estimate, because adipose tissue does not generate creatinine the way muscle does. Many institutions therefore specify ideal or adjusted body weight above a defined threshold. This calculator uses whatever weight you enter, without adjustment, so the choice is yours to make and to state.
Cockcroft-Gault Versus eGFR
| Cockcroft-Gault | CKD-EPI eGFR | |
|---|---|---|
| Reports | Creatinine clearance | Glomerular filtration rate |
| Units | mL/min | mL/min/1.73m² |
| Uses weight | Yes | No |
| BSA-normalised | No | Yes |
| Typical role | Drug dose adjustment | CKD staging and monitoring |
They answer related but distinct questions, which is why both remain in routine use rather than one having displaced the other.
Where This Calculation Matters
- Renally cleared drugs — anticoagulants, several antibiotics, and many others carry label thresholds expressed in Cockcroft-Gault mL/min.
- Older patients — the (140 − Age) term makes explicit how much clearance declines with age even when creatinine looks unremarkable.
- Teaching pharmacokinetics — the formula's linear and reciprocal terms make dose-adjustment logic unusually easy to reason about.
How to Use This Calculator
- Enter Age (years) — must be under 140 for the equation to return a positive value.
- Enter Weight (kg), applying whichever weight convention you intend; the calculator does not adjust it.
- Enter Serum Creatinine (mg/dL). Divide a µmol/L result by 88.4 to convert.
- Select Sex to apply the 0.85 factor for female.
- Select Calculate for the clearance in mL/min with the substituted equation shown.
Related Calculations
Run the same creatinine through the eGFR Calculator to see how the two estimates diverge, or see the Medication Dosage Calculator for the weight-based side of dose arithmetic.